1. Field of the Invention
The present invention relates to a magnetic recording medium, more specifically, to a magnetic recording medium which has a back coat layer excellent in surface smoothness and durability and is excellent in electromagnetic conversion property.
2. Disclosure of the Related Art
Conventionally, magnetic recording media have a magnetic layer on one surface of a non-magnetic support, and have a back coat layer on the other surface of the non-magnetic support in order to improve the running durability thereof and others.
In recent years, the recording density of magnetic recording medium has been desired to be made high in order to cope with an increase in the quantity of recording data. In order to make the recording density of the medium higher, the recording wavelength thereof has been made shorter and the magnetic layer has been made thinner. As the recording wavelength is made shorter, the magnetic layer surface is required to be made smoother from the viewpoint of spacing loss.
In the case that the magnetic layer is made thin, the surface roughness of the support is reflected on the surface of the magnetic layer so that the smoothness of the magnetic layer surface is damaged. Consequently, the electromagnetic conversion property of the magnetic layer deteriorates. For this reason, a non-magnetic layer is formed as an undercoat layer on the surface of the support, and then the magnetic layer is formed on this non-magnetic layer.
Japanese Laid-Open Patent Publication No. 2001-344737 discloses that, about a magnetic recording medium, a non-magnetic layer contains carbon black treated with at least one kind of anionic surfactant selected from carboxylic acid amine salts and phosphate amine salts.
Japanese Laid-Open Patent Publication No. 2002-312922 discloses that, about a magnetic recording medium, a magnetic layer contains ferromagnetic powder treated with at least one kind of anionic surfactant selected from carboxylic acid amine salts and phosphate amine salts.